1. Field of the Invention
The present general inventive concept relates to an audio reproducing system, and more particularly, to a wide mono sound reproducing method and system to widen mono sound, using 2 channel speakers.
2. Description of the Related Art
Generally, mono sound is reproduced through a single channel, but recently technology for synthesizing virtual stereo sound from mono sound has been under development.
Technology related to a mono sound reproduction system is described in U.S. Pat. No. 6,590,983 B1, entitled “Apparatus and method for synthesizing pseudo-stereophonic outputs from a monophonic input.”
FIG. 1 is a block diagram illustrating a conventional mono sound reproducing system. Referring to FIG. 1, a signal M is provided to a left all-pass filter 102 and a right all-pass filter 104. The left all-pass filter 102 is a phase lead filter that generates a leading phase shift of +45 degrees. The right all-pass filter 104 is a phase lead filter that generates a leading phase shift of −45 degrees. The output of the left-all pass filter 102 is provided to a first input of an adder 120 and a non-inverting input of an adder 122. The output of the right all-pass filter 104 is provided to a second input of the adder 120 and an inverting input of the adder 122. The output of the adder 122 is provided to a non-inverting input of an adder 126.
The output of the right all-pass filter 104 is also provided to an input of a perspective filter 124. The output of the perspective filter 124 is provided to an inverting input of the adder 126 and a second input of an adder 128. Also, the output of the left all-pass filter 102 is provided to a non-inverting input of the adder 126 and a third input the adder 128. The output of the adder 128 is provided to a high-pass filter 108 and a first input of an adder 106. The output of the adder 126 is provided to a high-pass filter 110 and a second input of the adder 106. The output of the adder 106 is provided as a low-pass filter 109.
The output of the high-pass filter 108 is provided to a first input of an adder 112, and the output of the low-pass filter 109 is provided to a second input of the adder 112. The output of the adder 112 is provided to an input of a left channel output amplifier 116, and the output of the left channel amplifier 116 is provided to a left channel output.
The output of the high-pass filter 110 is provided to a first input of an adder 114 and the output of the low-pass filter 109 is provided to a second input of the adder 114. The output of the adder 114 is provided to an input of a right channel output amplifier 118, and the output of the right channel amplifier 118 is provided as a right channel output.
Accordingly, the conventional wide mono sound reproduction system as illustrated in FIG. 1 processes a differential signal component generated from left and right input signals in order to generate a stereo sound image. The differential signal is processed by equalization characterized by audible frequency amplification of a low band and high band. The processed differential signal is coupled (i.e., added) with the left and right input signals, and the added signal generated from the original left and right signals.
Accordingly, in the conventional wide mono sound reproduction system, input mono sound is divided into different frequency bands, and levels of the divided bands are corrected and are then recombined. However, since a head and earflap of a listener, which perform important roles in recognizing a direction of a sound source, are not considered at all, performance of the conventional wide mono sound reproduction system is poor. Also, since the conventional wide mono sound reproduction system changes phases when generating two decorrelated signals from the input mono sound, a timbre can be changed.